Robust estimation of ability in the Rasch model

Estimating ability parameters in latent trait models in general, and in the Rasch model in particular is almost always hampered by noise in the data. This noise can be caused by guessing, inattention to easy questions, and other factors which are unrelated to ability. In this study several alternative formulations which attempt to deal with these problems without a reparameterization are tested through a Monte Carlo simulation. It was found that although no one of the tested schemes is uniformly superior to all others, a modified jackknife stood out as the best one in general, it was also super efficient (more efficient than the asymptotically optimal estimator) for tests with forty or fewer items. It is proposed that this sort of jackknifing scheme for estimating ability be considered for practical work.This research was funded through a grant from the Law Enforcement Assistance Administration (78-NI-AX-0047) to the Bureau of Social Science Research, Howard Wainer, Principal Investigator. We would like to thank Ronald Mead, Anne Morgan and James Ramsay for kind, generous, and invaluable help at various stages of the project.     

Effective random seeding of random number generators

To obtain different sequences of values from a random number generating algorithm, we must start with different seed values or discard a variable number of initial samples. For maximum independence among sequences, differences must include the lowest order seed bits, and some generators require one to wait many samples for differences to propagate to the significant bits. While it is straightforward to generate two statistically independent sequences, it is surprisingly difficult to generate three or more such sequences.     

Selective involvement of the auditory-verbal modality in an acquired communication disorder: Benefit from sign language therapy

A 39-year-old female suffered bitemporal infarctions and exhibited an unusual behavioral syndrome of muteness and impaired auditory comprehension, with milder aphasic deficits in reading and writing. The anatomic basis of this modality-selective communication disorder appeared to involve both peripheral perceptual and motor as well as “central” language mechanisms. The patient's ability to communicate was greatly aided by instruction in Amerind and Ameslan Sign Language, in which she learned more than 100 signs. Patients whose acquired language deficits spare modalities of input or output may be ideal candidates for sign language therapy.     

Right-left confusion in the adult: A verbal labeling effect

Directional judgments are typically slower when relative location is described by the words “east” and “west” or “right” and “left” than when described by the words “north” and “south” or “up” and “down.” A series of experiments are reported that disentangle verbal from perceptual encoding explanations for right-left difficulty. Overall, our results support a verbal encoding explanation for right-left confusion in the adult. Experiments 1-3 demonstrate that in a response-differentiation task, it is response to the labels “north,” “east,” “south,” and “west” that is responsible for right-left confusion. In addition, Experiments 4-6 demonstrate that right-left difficulty in a mirror image discrimination task is contingent on the use of directional labels. (The data also suggest that it may be more difficult to deal with “up,” “down,” “left,” and “right” than with “north,” “south,” “east,” and “west”) The data are interpreted as inconsistent with a bilateral symmetry explanation for right-left confusion.     

The effect of phonemic processing on the retention of graphemic representations for words and nonwords

The three experiments reported in this study were each conducted in two phases. The first phase of Experiment 1 involved a same-different comparison task requiring “same” responses for both mixed-case (e.g., MAIN main) and pure-case (e.g., near near) pairs. This was followed by Phase 2, a surprise recognition test in which a graphemic effect on word retention was indicated by the superior recognition accuracy obtained for pure-case compared with mixed-case pairs. The first phases of Experiments 2 and 3 involved pronounceability and imageability judgment tasks, respectively. Graphemic retention was assessed by contrasting recognition accuracy for letter strings presented, during Phase 2, in their original Phase 1 case, with letter strings presented, during Phase 2, in. a graphemically dissimilar new case. The experiments provided evidence that there was minimal retention of the graphemic representations from which the phonemic representations of words are generated and, further, that the locus of this effect is probably postlexical. Nonwords were recognized more accurately than words in all three experiments. The latter result was attributed to differences between nonwords and words in both graphemic retention and semantic distinctiveness.     

Perception of movement in American Sign Language: Effects of linguistic structure and linguistic experience

In order to reveal the psychological representation of movement from American Sign Language (ASL), deaf native signers and hearing subjects unfamiliar with sign were asked to make triadic comparisons of movements that had been isolated from lexical and from grammatically inflected signs. An analysis of the similarity judgments revealed a small set of physically specifiable dimensions that accounted for most of the variance. The dimensions underlying the perception of lexical movement were in general different from those underlying inflectional movement, for both groups of subjects. Most strikingly, deaf and hearing subjects significantly differed in their patterns of dimensional salience for movements, both at the lexical and at the inflectional levels. Linguistically relevant dimensions were of increased salience to native signers. The difference in perception of linguistic movement by native signers and by naive observers demonstrates that modification of natural perceptual categories after language acquisition is not bound to a particular transmission modality, but rather can be a more general consequence of acquiring a formal linguistic system.     

Institutional rationality: The complex norms of science

The claim is made that the norms for justified belief in science require a complex structure of practices and institutional arrangements, that these arrangements have a history which, at crucial junctures, are subject to severe stress, that such severe stress puts at issue the whole epistemic structure of science, and that at present science faces one of these periods, and its future is in doubt.     

Acquisition of probabilities in anticipatory appraisals of stress

Processes involved in predicting stressor events were examined from the perspective of ‘associative memory models’. Subjects were exposed to alphabetic letters which supposedly represented electrical resistors used in audio equipment, in the guise of marketing research. Each letter presentation was followed either by a burst of aversive white noise, signifying ‘resistor failure’ during a brief surge of current, or by a green light, signifying ‘resistor effectiveness’. After a programmed series of presentations, subjects were asked to make several judgments about each resistor; analyses of these judgments focused on the comparative influence exerted by the alternate stimulus events. Regardless of the type of judgment (e.g. probability of future noise, frequency of earlier silent outcomes, and so on), the determining stimulus property was the cumulative frequency of earlier aversive outcomes. Moreover, the dominance of this property was not altered by manipulations designed to elevate the salience of equally relevant benign outcomes. Results were discussed with reference to models of categorical memory and predictive confidence. Circumstances under which stress predictions may be especially inaccurate were considered, as were implications of the present findings for studies of differences in categorical-frequency memory processes associated with ‘depresed mood’.